need help with wiring a speaker cab.

[zippy]

hey folks! i'm new in these parts so please bear with me.
i have the 12" Jensen speaker from a 1947 Hammond M organ. i'd like to use that speaker to make a 1x12 extension cab, but i'm not sure how to wire it. there aren't just 2 wires coming from the magnet, there's 4. i'm trying to find out if anyone would know about how to wire it a input jack. also, if pics would help, i'd be happy to put them up. i don't know if it helps, but here's a link to the schematic. Hammond M Schematic thanks.

[Rob S]

Hi,

Do you have the amplifier as well?

If you look at the bottom left of your schematic you'll see that the power supply energises the speaker electromagnet (1000 ohm winding) and would appear to have 115V D.C. across it. I seem to remember they used this arrangement in old radios and the magnet coil would help smooth any ripple on the H.T. instead of a choke.

Unfortunately it'll be more trouble than it's worth without the original amp.

If you do use it, the 115V looks a bit excessive to me - start small & good luck.

Rob.

[zippy]

thanks for your help!

i do have the amp as well. my original plan was to use the whole unit and convert to a guitar amp, but i figured doing the ext cab thing would be easier.

[Enzo]

That is an electrodynamic speaker, also called a field coil speaker. All the speakers we use today are permanent magnet speakers. But field coils were common back then. There si no magnet in your speaker, the field coil must be energized to make a magnetic field for the voice coil to push against.

I don't think 115v is excessive, I have seen plenty of them running on twice that. Considering it is a 1000 ohm coil, that is only 115ma running through it.

You COULD remote the speaker, but you either have to run the field coil supply out to it, or make a supply. I did that as a kid - made a speaker cab with a power cord for the field coil supply.

Note that the field coil completes the circuit to the center tap of the power transformer, so it has to be there, either as itself or as a 1000 ohm power resistor. 115v @115ma is 13 watts and some, so such a resistor would have to be 25-30 watts at least.

In your schematic, the voice coil is where you see it like always, the other two wires are the field coil, and they are down at the bottom in the power supply.

[carl gigun]

thought I'd mention that jensen field coil speakers often fetch more on ebay than the permanent magnet jensens in later hammond Ms. The permanent magnet jensens in these sometimes have whizzer cones and generally have model numbers unfamiliar to guitar players which seems to keep their price down. Selling it leaves the amp with a hole in it's circuit though so they may be better kept together.

Also hammonds are often worth more than other old organs. As an organ it's probably worth a few hundred bucks, the catch being you need a local buyer because they're huge and heavy. Project amps can be found for a lot less than that, so you could be back to where you are plus have some money in your pocket.

[Mars Amp Repair]

Electromagnetic speaker

Hello,
I don't know if anyone mentioned it, but you'll have to rectify & filter the voltage for that electromagnet in the old Hammond speaker. If you try to pump AC voltage into it, it will hum.
The old designs from the 40's actually used the electromagnet in the speakers as the choke in the powersupply. Kind of a double duty.
Hope that's helpful if you didn't know. glen Mars Amp Repair.

thanks for your help!

i do have the amp as well. my original plan was to use the whole unit and convert to a guitar amp, but i figured doing the ext cab thing would be easier.